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What is Cantharidin Toxicity?

Cantharidin, a toxic substance secreted by the blister beetle, typically contaminates alfalfa hay. There are at least 200 different species of blister beetles, each having their own characteristics. A common genus is known as the Epicauta. Blister beetles can grow as large as 1.5 inches long, and can be a variety of colors such as gray, brown, or black. This beetle has long legs with sharp claws upon the tarsus that are spiny. It also has a narrow thorax six abdominal sections underneath.

Commonly found in alfalfa hay, the blister beetle can infect horses by ingestion and cause toxicosis. Cantharidin is an odorless terpenoid that has no color. This toxic terpenoid is also present in other types of beetles. Cantharidin is also toxic to humans, and horses only need to ingest 1mg/kg of their total body weight; even half of that can be fatal. This substance is resistance to heat and drying, which causes it to be a challenge to remove during the processing of the alfalfa pellets or bales.

Cantharidin is also found as an ingredient in medications, although it does have potential to cause negative effects. When cantharidin is compounded correctly it can be effective when used topically by a medical professional. Patients with skin conditions such as warts as well as molluscum have had success with medications with cantharidin as an ingredient.

Cantharidin toxicity in horses occurs when horses ingest a specific type of beetle, known as the blister beetle, which is commonly found in alfalfa hay. The blister beetle secretes the toxin known as cantharidin, and can be fatal if horses ingest a toxic amount.

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Symptoms of Cantharidin Toxicity in Horses

Symptoms of blister beetle toxicosis can occur very soon after ingestion, typically within a six to eight hour time frame. Symptoms include:

Colic

Restlessness

Agitation

Diarrhea

The submersion of his muzzle into water

Irritability

Sweating

Depression

Dehydration

Fever

Oral ulcers

Types

Cantharidin is excreted not only by the blister beetle; however, the blister beetle is significant in the toxicity of horses since it is commonly found in the alfalfa hay they ingest. Other types of insects that secrete this toxic substance include:

Spanish Fly

False blister beetle

Cardinal beetle

Soldier beetle

Causes of Cantharidin Toxicity in Horses

Blister beetle toxicity is common in horses and can be prevented by either carefully inspecting alfalfa hay or avoiding it all together. Causes of blister beetle toxicity in horses include:

Beetles found in alfalfa hay

Acantholysis in the gastrointestinal tract

Acantholysis in the vesicles of the skin and mucous membranes

Alters mitochondrial metabolism

Inhibits protein phosphatase

Increases permeability of the endothelial cells

Diagnosis of Cantharidin Toxicity in Horses

If you suspect your horse is suffering from blister beetle poisoning, contact your veterinarian as soon as possible. The ingestion of the blister beetle and the rapid secretion of cantharidin can be fatal to your horse.

Your veterinarian will immediately begin examining your horse by looking at his clinical signs. He will take blood work, urinalysis, and biochemistry profile for initial assessments. Your veterinarian may also perform laboratory testing on several other areas. Your horse’s serum calcium content will be evaluated, which in poisoning may be very low. Hypocalcemia is one clinical sign of cantharidin poisoning. In addition to the serum calcium content being abnormally low, the horse’s concentration of serum magnesium may be low as well. Creatinine kinase may be elevated in times of cantharidin toxicity. Serum urea nitrogen levels may also be tested, as these may be elevated in your horse. Typically, laboratory findings will reveal hypocalcemia, azotemia, and hypomagnesemia.

Your veterinarian may also use high-pressure liquid chromatography testing to reveal cantharidin toxicity. This is commonly performed in horses that are deceased. Owners that find their horse deceased can find the reasoning by submitting a urine sample, or the veterinarian can remove the stomach contents for testing.

Treatment of Cantharidin Toxicity in Horses

Unfortunately, there is no antidote for cantharidin toxicity. Treatment will be solely focused on systematic treatment and the attempted removal of the toxins from the horse’s system. Treatment methods may include:

IV Fluids

Your veterinarian will administer intravenous fluids to rehydrate your horse. IV fluids help the horse restore electrolytes as well. These fluids also help the body flush out any toxins and promote proper kidney function through urination.

Pain Medication

Your veterinarian may carefully administer NSAIDs. NSAIDs can harm your horse’s kidneys, though, if he is dehydrated. Mineral oil may be given to help the gastrointestinal tract. Activated charcoal may also be given to help absorb the toxins, and there are other types of absorbents may be recommended by your veterinarian. Supplementing your horse with magnesium and calcium may be helpful as well, but this will need to be for a longer time period.

Monitoring

Your horse will be monitored by your veterinarian. He will monitor his blood work and his urination, and do frequent checks on his vital signs. Monitoring will also be symptomatic, and the veterinarian will address any issues as they arise within your horse. Also, once the horse is home, he will need to be monitored by you by resting in his stall.

Recovery of Cantharidin Toxicity in Horses

Unfortunately, many horses succumb to cantharidin poisoning. If your horse was able to be treated, he may have a chance for recovery. The veterinarian will determine if your horse is making any progress. If you are able to take your horse home, the veterinarian will give you instructions on how to properly care for your companion.

In order to prevent cantharidin poisoning, be sure to always closely examine his alfalfa hay. Many owners choose to not feed their horse any at all, as they feel being safe is better than sorry. Blister beetles are very hard to be seen within the hay, even after processing. The first cutting of alfalfa hay typically does not contain the beetles since they usually do not come out until the late spring and early summer months.